Effects of barium and ion substitutions in artificial blood on endocochlear potential

Previously, a qualitative assessment was made (Marcus, D.C. (1984): Am. J. Physiol. 247, C240-C246) of the ion-selective properties of the cells bounding the cochlear duct by observing the effects of ion substitutions in the perilymph on the transepithelial potential difference (endocochlear potential; EP). Contributions by the marginal cells of the stria vascularis to the observed changes in the EP may have been masked, however, due to their 'isolation' from the perilymph by a continuous layer of basal cells. Since the ionic milieu of the basolateral membranes of the marginal cells is controlled more directly by the blood supply than by the perilymph, we report here on the effects of ion substitutions via vascular perfusion. Elevated K (substituted for Na or N-methyl-D-glucamine; NMDG) or Ba caused marked depression of the EP. Decreased Na or Cl (replaced by NMDG and gluconate, respectively) also depressed the EP. These changes in the EP were distinctly different from those observed previously by perilymphatic perfusion, and were interpreted in terms of a modified model of the strial marginal cells.